Vaporizing temperate peatlands

Peat decomposition causes soil subsidence and is responsible for greenhouse gas emissions. Peat forms under wet conditions, but in the Netherlands peatlands have been drained (by humans) for about a thousand years. The drained peat pastures are mainly being used for dairy production. In the drained peat soils with lower groundwater levels, oxygen enables high rates of peat decomposition. This peat decomposition has caused most peatlands to sink below sea level, and currently, these peatlands are still subsiding (on average 6 mm per year). Peat decomposition is also a major source of greenhouse gas emissions: in the Netherlands, about 4% of greenhouse gas emissions emerge from vaporizing peatlands. Rewetting peat could reduce decomposition rates and associated greenhouse gas emissions. This dissertation focuses on the effects of rewetting peatlands using water infiltration systems. Here, peatland hydrology, CO2 emissions and microbial soil processes are play a central role. Is a resilient future for peatlands within close reach? Under normal conditions, the hydraulic conductivity of peat is too low to maintain steady groundwater levels by ditch water infiltration during drier periods. The aforementioned water infiltration systems consist of underground drainage pipes that transport ditch water to the centre of a peat pasture. In this dissertation it is demonstrated that under certain conditions and to a certain extent, these water infiltration systems (1) successfully raise groundwater levels, (2) substantially reduce CO2 emissions from peat, and (3) influence microbial decomposition processes in the soil. Also, the thesis presents (1) the foundation for a new, national model to estimate peat degradation under aerobic conditions, (2) an accessible method to measure microbial decomposition processes in the soil, (3) a high-frequency dataset of CO2 fluxes from peat pastures determined using automatic flux chambers, and (4) new relationships to estimate annual CO2 fluxes based on average groundwater levels. The chapters in this thesis may contribute to improving the monitoring of greenhouse gases from peat. Throughout the dissertation, the automatic chambers play a major role in measuring emissions from peat. The thesis also discusses how alternative methods could be used to improve the understanding of peat degradation processes and the associated emissions. For example, the second chapter lays the foundation for a national model (SOMERS) to estimate greenhouse gas emissions from peat (and emission reductions), the third chapter lays the foundation for a direct measurement method for degradation processes and emissions at different soil depths, and the fifth chapter shows how groundwater levels can be used as an indicator for emissions. Furthermore, the insights presented on emission reduction may help in practical decision-making by provinces and water boards. The Dutch government has decided in the Climate Agreement that CO2 emissions from peatlands must be reduced by one megaton (25%) by 2030. The results in the thesis illustrate to what extent the implementation of water infiltration systems can contribute to this reduction. Besides water infiltration systems, other solutions are also available that lead to emission reductions (e.g., wet crops and nature restoration), each having their pros and cons. For policymaking, not only the reduction of peat degradation, soil subsidence and CO2 emissions play a role, but also economic feasibility, farmers' interests, biodiversity, soil contamination, water quality, water availability, nitrogen emissions and landscape culture should be taken into account. Towards harmony in (agri)culture and peat preservation! This PhD thesis is part of the Netherlands Research Program on Greenhouse Gas Dynamics in Peatlands and Organic Soils (NOBV). Within this program, high-tech peatland measurement locations have been set up to quantify peatland greenhouse gas emissions, and effects of different (land management and/or hydrological) treatments on these emissions.